Gases such as helium, argon, neon, krypton and xenon have the potential to be used in a wide range of manufacturing processes. An example of one such process is the production of semiconductor devices such as semiconductor integrated circuits, active matrix liquid crystal panels, solar cells panels and magnetic discs. During the manufacture of the semiconductor devices, systems for generating plasma in a noble gas atmosphere under reduced pressure are utilized for various treatments of the semiconductor devices with the plasma, for example, a sputtering system, a plasma CVD system and reactive ion etching system. In addition, noble gases are used in other applications such as metal atomization processes, cold spray forming, cooling, and shield gas applications.
Most of the aforementioned applications use large quantities of noble gas such as helium. The cost of using helium would be prohibitive without some form of recycle system for the used gas. In order to recycle the noble gas to the application, impurities such as water, nitrogen, oxygen, carbon dioxide, methane carbon monoxide, hydrogen and particulates from furnace off gas must be removed from the used gas.
Various purification systems have been proposed in the prior art. Such systems include helium recycle with membrane, thermal swing adsorption (TSA), pressure swing adsorption (PSA) and/or copper oxide technology. The choice of purification technology depends on the type of process, the off-gas impurities and inlet feed gas compositions. For example, if the only contaminant in the noble gas is oxygen, then a copper oxide getter could be used to take out oxygen. However, if only water is present, then a dryer operating in TSA mode may be used. If both water and oxygen are present, then a combination of copper oxide getter and dryer may be used for purifying the noble gas (e.g., helium).
Ohmi et al., in U.S. Pat. No. 6,217,633 B1 discloses a process and an apparatus for recovering a noble gas (defined as one or more of Xe, Ar, Kr Ne or mixtures thereof) contained in an exhaust gas from a noble gas employing unit. In particular, the invention of Ohmi et al., provides a process and apparatus for recovering a noble gas at high recovery and predetermined purity from a noble gas employing system such as plasma treating system. The noble gas employing system operates under reduced pressure. The recovery unit receives intermittent feed gas based on the inpurity concentrations in the used gas (exhaust gas) leaving the noble gas employing unit. The impurities include oxygen, nitrogen, water, carbon monoxide, carbon dioxide, carbon fluoride, hydrogen and various film-forming gases. If the impurity concentrations are beyond certain limits, then the used gas is exhausted as waste instead of being sent to the recovery unit. The choice of venting exhaust gas from the noble gas employing system as waste or sending to the recovery unit depends on the content of impurity components contained in the exhaust gas or on the running state of the noble gas employing system.
U.S. Pat. No. 5,390,533 describes a process for pressurizing a vessel for integrity testing using helium as the tracer gas. The invention also discloses the recovery and purification of helium for reuse. The process for purifying the gas stream comprises drying the gas stream using a membrane dryer that permeates water. The water depleted raffinate from the membrane dryer is sent to a membrane separator for further purification. Helium selectively permeates the membrane in the membrane separator to produce a helium enriched permeate stream. The helium-depleted raffinate stream is sent to a membrane stripper stage to obtain a purge stream to purge water from the membrane dryer.
Behling et al., in U.S. Pat. No. 6,179,900 B1 disclose processes for the separation/recovery of gases where the desired component to be separated from the mixture is present in low molar concentrations and/or low to moderate pressures. A combined membrane/PSA process is utilized for the separation/recovery of gaseous components which are present in the stream at low pressures and/or molar contents. The membrane unit is positioned at the upstream end of the PSA process.
U.S. Pat. No. 6,092,391 discloses helium recycling for optical fiber manufacturing in which consolidation process helium is recycled either directly for use in consolidation at high purity or recycled at lower purity for usage in draw or other processes requiring lower helium purity. In addition, integrated processes for recycling helium from two or more helium using processes in the optical manufacturing process are also disclosed.
U.S. Pat. No. 5,707,425 to D'Amico et al.,describes a process that is directed to the recovery of helium gas from gas streams containing about 25% by volume or more of helium. Two PSA processes are used in a serial arrangement. Stoner et al. in U.S. Pat. No. 5,632,803 discloses a hybrid membrane/PSA process for producing a helium product stream at a purity in excess of 98.0% from feed stock containing anywhere from 0.5 to 5.0% helium. The membrane is placed upstream of two PSA processes, and all of the separation units are arranged in a serial configuration.
U.S. Pat. No. 5,377,491 describes a coolant recovery process for a fiber optic cooling tube. The process uses a vacuum pump/compressor to remove cooling gas from the cooling tube, remove particulate and contaminants and then return the coolant gas to the fiber optic cooling tube. Purification equipment such as PSA, dryer and membrane are mentioned for the removal of water and oxygen.
U.S. Pat. No. 5,158,625 discloses a process for heat treating articles by hardening them in a recirculating gas medium which is in contact with the treated articles. According to one of the embodiments, used helium is collected and sent to a membrane unit to produce purified helium at low pressure. The purified helium from the membrane unit is sent to a dryer prior to reuse. In another embodiment, the used/contaminated helium is mechanically filtered, then oxygen is removed via controlled addition of hydrogen for catalytic production of water, after which the gas is possibly cooled and dried for reuse. In another embodiment, hydrogen is used for regenerating a catalyst used for trapping oxygen. Also, in a further embodiment, PSA or TSA is used for removing oxygen and water vapor, after which the gas is cooled and dried.
Knoblauch et al., U.S. Pat. Nos. 5,089,048 and 5,080,694 disclose PSA processes, arranged in a serial configuration, for extracting helium from a relatively helium poor gas mixture, e.g., natural gas containing 2-10% helium. The first PSA process is used for helium enrichment and the second PSA process is used to achieve target helium purity of at least 99.9%.
Choe et al., in U.S. Pat. No. 4,717,407 discloses a helium recovery system by integrating permeable membrane separation with “non-membrane” separation techniques. The patent refers to PSA applications as one of the possible “non-membrane” separation operations. Czarnecki et al., U.S. Pat. No. 4,675,030, disclose a method of purifying helium gas contaminated with air, water vapor and traces of carbon dioxide. The contaminants constitute less than about 10% by volume. According to this invention, the process contaminated helium gas is compressed and cooled to condense the bulk of the water vapour then the dried gas is passed to a first membrane unit to produce high purity helium for reuse. The retentate from the first membrane unit is passed to a second membrane unit. The permeate of the second membrane unit is recycled back to the first membrane unit, whereas, the retentate of the second membrane unit is discarded as waste.
U.S. Pat. No. 4,238,204 outlines an improved selective adsorption process for the recovery of a light gas, such as hydrogen or helium, from a feed gas mixture by utilizing a membrane permeator unit selectively permeable to the light gas being collected. Specifically, this invention utilizes a hybrid PSA/membrane process to recover helium. The PSA process is placed upstream of the membrane unit, and the effluent of the PSA process during the adsorption is collected as product helium. The exhaust gas from the PSA process, obtained during the purging step, is sent to a membrane unit for additional further purification. The permeate from the membrane unit is recycle to the PSA feed. The non-permeated gas mixture comprised mainly of the impurities and a small proportion of the helium is recovered for other use or disposed of as waste.
The prior art processes suffer from low helium purity and per pass recovery when using a single stage PSA process alone to recover helium. In addition, in order to achieve enhanced helium purity and recovery, the prior art typically utilized a combination of PSA and membranes, or PSA and cryogenic systems, or serial arrangements of PSA processes using different number of beds and PSA cycles. Consequently, using the prior art, the capital and operating costs are too high to promote the use of recovery systems to conserve noble gas such as helium.